Most flexographic printing plates available today are extremely fragile before they are imaged and cured. The active layer of the plates is typically made from a polymer which, prior to exposure and curing, is in a gelatinous state. Consequently, any handling of the plate prior to curing can lead to degradation in its image retention properties. It is desirable, for this reason, to minimize the invasiveness and the amount of any handling procedures. This is even more true for digital flexographic plates which have an ablative opaque coating on top of the photo-polymer.
For the above reasons, flexographic plates are frequently transported and stored with a protective coating over the active layer. Although the coating protects the active layer of the plate, it must be removed prior to imaging. To minimize any potential damage from handling, it is desirable to maintain the coating on the plate until immediately prior to imaging. A drawback associated with the protective covering is that it may be difficult and/or may require excessive handling to separate from the plate.
As such, there exists a need for a device which is capable of both rigidly securing a flexographic plate so that its protective coating may be removed and delicately conveying the plate onto an imaging cylinder without excessive handling.
In, general the prior art techniques for loading printing plates onto imaging and printing cylinders have been mechanical in nature employing cylindrical rollers. Such techniques are described in U.S. Pat. Nos. 4,281,922, 5,555,812 and 5,634,406. Disposed on either side of the plate, the rollers compress the plate between them and convey it onto the printing cylinder. Such techniques are not suitable to convey uncured flexographic plates because the compression of the plate between the rollers could easily damage the plate's active layer, impairing its image retention properties.
Air tables and devices for effecting the movement of articles using fluids are well known. (See, for examples, U.S. Pat. Nos. 4,568,223 and 3,734,567). However, these devices do not disclose the use of pneumatic air tables alone to convey printing plates. Furthermore, these devices do not disclose the use of the pneumatic tables as both a securing device and a conveying device.
Accordingly, it is an object of the present invention to provide a flexographic plate imaging device equipped with pneumatic air table apparatus which is capable of delicately conveying a flexographic plate onto an imaging cylinder with a minimum amount of physical handling.
It is a further object of this invention to provide a flexographic plate imaging device equipped with a pneumatic air table which is capable of rigidly securing a flexographic plate so that its protective coating may be removed prior to the plate being conveyed onto an imaging cylinder.
It is another object of this invention to provide a method for transferring plates from a loading table to the imaging cylinder of a flexographic imaging device.